Even if your home wasn’t hit by a storm, a leak or small flood could leave you exposed to mold damage. Hidden mold can eat away at a building’s structure for years until it’s too late, while triggering asthma and allergies, warns UL, the product-testing company formerly known as Underwriters Laboratories, in a press release.

To help protect your home from mold damage, play detective. If you can see damp spots, surface mold, or there’s a musty smell around, you could have mold. If your home has suffered from a recent flood, check all surfaces for moisture and stains.

Figure out how extensive the mold problem is—whether it’s on the surface or may have penetrated the walls, says Marie Leonard, owner of Marie’s Home Improvement, in Westford, Mass. If it’s inside the walls, you’ll have to replace the materials, such as drywall or wood paneling.

There are different ways to test for mold, but here’s one you can do easily: If you see discoloration on a wall, put a drop of bleach on the stain; if the stain bleaches out, that’s a hint there’s mold in the wall. The Federal Emergency Management Administration has a chart to help homeowners gauge the extent of the problem and whether they should call in a pro.

“If a large water problem has occurred, such as flooding, and walls and floors have been wet for an extended period of time, I would always recommend calling in a professional,” says Leonard, author of Marie’s Home Improvement Guide.

“We advise consumers to follow the ‘Four Ds’ to mitigate and defend against mold after a flood: Dry, Discard, Deactivate, and Defend,” says Brian Bacik, CEO of Planet People, a manufacturer of cleaning and mold-prevention solutions.

Planet People’s checklist includes “drying” the area quickly after the flood and “discarding” any soggy items you can, such as carpet and ceiling tiles. “Deactivate” means neutralizing mold with a disinfecting solution, such as bleach. Finally, “defending” your home against a repeat involves this three-step process:

Level the ground around your foundation so water flows away from your home.

Run a dehumidifier indoors to keep the humidity below 50%.

Monitor the levels of dampness with a hygrometer, an inexpensive device you can buy at a hardware store.

Here are few suggestions to handle everyday and disaster-level mold outbreaks:

Dry early.

Water damage turns to mold in three to seven days. Get the water out with a water pump or shop vacuum, open doors and windows, and use fans to circulate air and dry the flooded area. Start the drying process in the first 48 to 72 hours, and save yourself a lot of grief and repair bills.

Hidden mold can eat away at a building’s structure for years until it’s too late, while triggering asthma and allergies.

When in doubt, throw it out.

Mold could be lurking where you don’t see it, so junk anything that hasn’t dried quickly, smells moldy, or looks porous. UL recommends taking out right away all damaged carpet, drywall, ceiling tiles, and pressed-wood furniture. Less-porous materials such as lumber can be scrubbed and pressure-washed, and non-porous items such as solid countertops and flooring can be set aside to clean later. Above all, clean them while wet—instead of letting them dry first, so bacteria can’t settle in—and be thorough, before disinfecting them.

Know when to DIY—or not.

The Environmental Protection Agency (EPA) has guidelines for cleaning mold in the home, including how to protect yourself from exposure while working. But it also recommends calling in a professional if you are dealing with delicate items or those with sentimental value, or if the job involves a larger area—more than 10 square feet, or three feet by three feet.